Methane is known as a main cause of greenhouse effect and is 20 times more lethal than carbon dioxide in the same amount. However, simultaneously, methane has been in the limelight as one of the most important energy resources. In particular, methane is a main component of natural gas, and is available in large quantities, and as a result, is preferably desired to be used as fuel. However, since methane is present in a gaseous state at room temperature-atmospheric pressure, it is difficult to transport and store methane, and a methane reservoir is considerably overlapped with an oil reservoir, such that usage depends heavily on imports.
Methane is generally present in the gaseous state as described above; however, may be stored in a form of methane hydrate in the ocean's and earth's crust. The methane hydrate is a solid material containing methane molecules in a crystal structure of water molecules under conditions of low temperature and high pressure, and is known to be buried in quantity in the East Sea of Korea, and The Government Development Project Group found about 600 million tons of methane hydrates under the sea at about 100 km south from Ulleung Island in June 2005. This amount corresponds to domestic consumption of natural gas for about thirty years.
Development and utilization of the metal hydrate as new energy resources are currently being planned as a national project. However, since the methane hydrate is present as a solid in deep sea, it is difficult to apply existing methods of mining the natural gas. Therefore, development of a new mining technology has been demanded.
In addition, accompanying with the development of the mining technology, the methane hydrate is partially decomposed and melted in the seawater, such that a technology of measuring an amount of dissolved methane present in the seawater has also been demanded. In general, the measurement of the dissolved methane is performed by the following two steps:
A first step is to extract methane gas in a dissolved state as a methane gas in a gaseous state, and a second step is to quantify the extracted methane gas. Extraction of the gas in the dissolved state is mainly performed by using a headspace, by using purge-trapping, by using an equilibrator, and the like. The extracted methane is quantified by gas chromatography equipped with a flame ionization detector (FID) and a photo-acoustic infrared detector. These methods are advantageous in that since methane in air has significantly low concentration, there is a small possibility in polluting a sample, and detectors used for quantification are possible to measure the low concentration, and therefore, a measurement error is generally small. However, the methods of using the headspace or purge-trapping have problems in that it takes a long time for processing the sample, and accuracy in measuring the concentration is decreased in a step of extracting the dissolved gas (An and Joye, 1997). In addition, an amount of the sample required for the measurement is relatively large as 50 to 600 ml or more, which makes it difficult to repeat experiments.